The proposed research has two major components, which despite sharing common elements in their inception, are quite distinct in their overall objectives. High priority is being placed on a line of investigation whose object is to study processes leading to large scale rearrangements of the Escherichia coli chromosome. We are particularly interested in the interaction of redundant sequences within the chromosome to produce tandem duplications, deletions and translocations. For example seven highly homologous genes coding for ribosomal RNA are distributed around the E. coli chromosome. We have shown that these ribosomal RNA genes are "hot spots" for unequal recombination leading to tandem duplications and potentially to other rearrangements. In addition to extending our studies on the nature and consequence of this class of mutants, we wish to investigate other recurring rearrangements which point to "hot spots" the indentity of which is not known but which definitely are not rrn genes. The importance of our understanding unequal recombination has been underscored by the recently reported observations that resistance to antiproliferative drugs in cultured cells often involves gene amplification. The second major component of this proponent of this proposal has to do with the genetics of glycine tRNA in E. coli. Previous studies of missense suppression by us and by others have produced an extensive knowledge of the location, degree of redundancy and function of the structural genes for the three glycine tRNA species. We wish to extend our knowledge of one of these genes, glyU coding for tRNA Gly GGG, as fully as possible, elucidating its structure, the nautre of its expression, and the effect of various mutations on tRNA biosynthesis and on cellular processes. We also propose to develop the glyU missense suppression system as a tool for studying multiple base substitution mutations.